Sound-reproducing system



Aug. 15, 1939 I s. G, SEARS vscum) REPRODUCINQSYSLT'EI Filed Dec. 7, 19:56 2 Sheets-Sheet 1 100 A moo moo I A z/z/vcf (a v y .INVENTOR.

412W AT RNEYS.

' structed in accordance withthe invention;

Patented'AugQ 35,, E329 are? 2.16am sonua arrnonncnse sirsrnsr Steriing (in SEEKS, Garden @ity, N.

in, assignor to Dictograph Products flompany, line, New York, N. Y a corporation of Delaware lippiicationhecemher i, ices,- Seriala; men

a Qlaims. This invention relates to sound reproducing systems, and mcreparti'cularly to systems -designed'ior the reproduction of sound with 2. volume and quality adapted for use in the field served by loudspeakers but may also be used by persons hard of hearing.

More particularly, the invention relates to v devices for reproducing sound with high fidelity that are adaptedfor use inconjunction'with ordinary sources of sound to be reproduced, such whereby persons-using the devices may hear the sound with a desired effect.

The invention has for its object generally the provision of a system of the character indicated 1 which issmall and rugged and highly eiiici'ent fand maybe used to service persons of normal hearing and also persons hard of hearing. under certain conditions.

Another object'is to provide a device that is relatively smalt and light in weight and is of the Y propagating diaphragm whereby the quality of and the scope of inertia type for reactively driving the sound the sound reproduced is unaffected by pressure on the diaphragm. Y

vStill another object is to provide a devicethat may be used by persons hard of hearing in which the range may be varied to permit the user to select the sound perceived with adesired quality. Other objects of the invention will in'part be obvious and will in part appear hereinafter.

- The invention accordingly comprises thefeatures of construction, combination of elements and arrangement of parts, which will be :exe'm- 'plified inthe construction hereinafter set forth the invention will be-indicated intheclaims- For a fuller understanding of the nature and objects of the invention, reference should be had to. the following detailed description'taken inconnection with the v accompanying drawings, in.

. which:

section,

form of sound reproducing device that may 'be I used in the system of the present invention;

-Flg. 3 is a diagrammatic. chartshowingthe" volume-frequency characteristic of a device conj v with faulty hearing; Such devices are also found Fi .5 a a sectional View showing gnome:

Thep

showing a system embodying the in- Fig. 2is a, sectional view showing' a'modified ici- 17%1639) modification of aspeaking device that may be used in the system of the present invention; and 6 is a plan view of the device shown in Fig. A

When the constants of a sound reproducing a device are arranged to have relatively good efiiciencies in both the high frequencies and the low frequencies, the perceived efiect is said to be normal, a normal response characteristic being depicted in Fig. 3 by curve a in the drawings. m Such responseis approached in telephone receivers and loudspeakers, but has not been achieved with'reactively driven sound reproducing devices, as shown, for example, in the U. S. patent'to Reynold s, No. 1,630,028, dated May 2 2, it? 1927.

In accordance with the present invention, a. response characteristic satisfactorily approach-- ingnormal may-.be attained with reactively driven sound reproducing devices, when driving 2o relatively extended dlaphragms and employed in free air. In such case, the driven member advantageously has a mass comparable with that advantageous; Also, the performance of the device is substantially unaltered by the application 3 of pressure of external origin to the parts ofthe device, by-reason of the constancy of the air gap employed in inertia type of vibrating -mecha- While the dimensions ofzthe air gap are,

, of; course, periodically altered by small displace- '35 ments'when the parts of the mechanism are vibratin g,--it is seen the average width of the air gap is substantially a fixed quantity and is the characteristic of the'air gap of an inertia-device.

substan- 40 erformance ofthe device is hence tially' independent of 1 external pressure; Such device may accordingly be usedfor. the reproduction' of sound with. satisfactory perception characteristics in fields heretofore impossible of being serviced by sound reproducing devices, for '46 examp'le,.for reproducing sound. with a desired response in a sound absorbent medium. g

' Sound reproducing devices provided in accordance with the. invention are found to be practical for; reproducing sound in free air for those iii.

to bepractical as. bone conduction hearing aid devices when employing a. diaphragm extended fork with the coil 2 as indicated to increase the baffle effect, may. be used by persons hard of hearing by applying sufficient electrical energy to give a volume which overcomes the deficiency of the ear and to allow the user to adjust the tone characteristic or response range to suit the individual needs of the user, by proper placement over the ear.

A sound reproducing device, provided in accordance with the invention, may employ various constructions, for example, the size, shape, and electrical constants may be modified to accentuate the response of the device in certain regions, such as in the high frequencies, to compensate for the response imparted by baffling in order thereby to achieve a normal flat characteristic. Where a person of normal hearing is desirous of having sound reproduced with a flat characteristic under the unusual circumstances, for ex ample, when the sound is transmitted through an absorbent medium, the constants are altered to provide a peaked response to compensate for the absorption. Hence, it is seen that a substantially normal characteristic may be attained under substantially any condition of use.

The source of the electric impulses for electromagnetically driving the vibrating mechanism may be any suitable source, for example, the output of a phonograph which employs a magnetic pick-up, or the output of a radio, telephone, or other convenient source.

Referring now to the drawings, and particularly to Fig. l, H) denotes a source of primary electric impulses here represented as had from a magnetic pick-up of a phonograph. The device i is connected to a suitable amplifier symbolically denoted II, which supplies a coil I2 that may be the primary of a transformer having a secondary l3 for supplying current to a suitable electromagnetic driving means ductors 'H; the driving means being arranged to actuate a speaking device such as shown generally at R. r

The speaking device R, according to the present invention, is preferably disconnectably connected with the source of actuating current. Accordingly, conductors H lead to a plug-in device IS; a control switch l5 being preferably inserted in the connections. From the plug l6 lead conductors IT to a coil or winding I! which comprises the driving or actuating means for the system which comprises the vibrating mechanism that vibrates diaphragm or member S of the device R. This mechanical system has articulated members IS, 20, and 2i arranged to form a tuning is disposed between the prongs. One prong, namely, member 2|, is fixed to the diaphragm S so as to drive the same reactively; the system being disposed in a housing H that is secured to the diaphragm S. In this arrangement, the coil I8 is preferably mounted on a core member that is attached to the free prong I9, the core terminating short of the fixed prong 2| so that there is a relatively small air gap therebetween, as shown at 22. 1

The diaphragm S is preferably extended beyond the housing H to an extent which accomplishes the desired air coupling; for example, the diaphragm may be in the neighborhood of 2 inches in diameter. The driving system, in consequence, is relatively small and may be enclosed in a housing in the neighborhood of 1 /2 inches in length and inch in both width and height.

The volume-frequency response of the air coupled device shown in Fig. 1 is depicted in Fig. 3, which illustrates curves drawn so that the ordithrough connates represent volume, while the abscissa represent frequencies. The flat perception characteristic desired for persons of normal hearing is represented by the curve u. Where a diaphragm of extended surface is employed in a bone conduction device in accordance with the present invention, improved response is produced for the low frequencies by the action of the extended surface covering the external auditory canal. Persons of normal hearing using such an extended diaphragm would, in consequence, receive a pleasant and natural type of reproduction, in accordance with the curve u shown in Fig. 3.

This type of response will result from an instrument peaked in the neighborhood of 4000 cycles per second, as depicted in the curve 112, which represents the response in free air when used as described. However, if the device is not held in intimate contact with the external auditory canal, a response characteristic intermediate to the curves u and w is had, and is depicted in curve v. Satisfactory results, however, can be obtained with response characteristics with peaks located in the region of from 2000 to 6000 cycles per second. Response characteristic curves having such properties are shown in the drawings at w and It is important when accentuating frequencies in this region that so-called high frequency noise be reduced, such as record scratch and the like. The reduction of these noise frequencies, however, should be only to the extent which gives an agreeable tone value and not to an extent which affects the quality of the music or speech.

To introduce the desired response characteristics mechanically into the system shown in Fig. 1, the resonance characteristics thereof are so proportioned as to peak the response in accordance with the curve 10. This may be accomplished, for example, by stiffening the yoke or reed member 20. The ratio of high frequency to low frequency may be increased by increasing the stiffness in any suitable manner, for example, by altering the cross-section of the reed or yoke 20 to increase its thickness. Stiffness'being also dependent on the material employed, the desired increase may also be achieved by using harder material, or by the combined use of a harder material and an altered cross-sectional dimension. Also it will be readily understood that the area and stiffness of the diaphragm S may be altered to impart additional modification to the response characteristics. For example, the surface of the diaphragm S may be increased to increase the ratio of low frequency to high frequency energy in the sound response.

In the modification shown in Fig. 2, the vibrating surface of the diaphragm is not made plane but has a conical configuration. In this form of device, the relatively light but stiff surface is indicated at T. This may be made of any suitable material, such as a molded cellulose product with acetate base. The mechanical system which drives the diaphragm is shown as comprising articulated members I9, 20, and 2|, which form a tuning fork that is eleotromagnetically driven by a winding I8 supplied with actuating current through conductors H as in Fig. 1. The fixed prong member 2| is rigidly secured to the diaphragm near the apex by means of studs as indicated at 24. The free prong member has a support 25 thereon which supports the connections to which the terminals of the winding I8 are led and secured. Here, the members comprising the driving mechanism are not only stiffened, to a efiiciency preferably tions so as readily cloth, thatis secured about the periphery of the 7 conical diaphragm in any convenient manner.

in this form of device, the operation is substantially thesame as that shown in Fig. 1, the response characteristic being such as to give sound perceived withthe desired flat characteristic in consequence of the modification imparted by increasing the mass of the thereby making the response quite uniform throughout the audible region.

The circuit of the electromagnetic driving means is seen to comprise the windings i3 and it which are connected by the conductors ll. This circuit in order to operate with a maximum has matched impedances at is and it. Where it is desired to impart the response characteristics electrically to the transdriving system,

lating device of the present invention, this driv-- ing circuit is modified to shift the resonance char= acteristic to a point corresponding to the peak inthe curve to. This is accomplished by introducingsuitable elements of inductance and capacitance in the driving circuit as illustrated in Fig. Here, primary electric impulses correspondlations of a, radio carrier that is collected by an antenna it coupled to the amplifier ii that supplies a Winding l2. winding may be the primary of a transformer whose secondary-i3 its output through conductors it into the electromagnetic driving means comprising a winding it" of in the interestsci clearness of illustration in the drawings). 'llie circuit comprising windings it it" and conductors id is modified by the ductionor the elements of impedance which ay be accomplished in any one oi several ways, example, by introducing an element of intense Z in shunt with the winding'ii and an rent of capacitance it in series therewith, the in being chosen that the response characa preaches that oi the in the modification of Figs. and 6, an arngement for a speaking device similar to that lg. 31, but providing the plug-in connections to housing H of the device, is shown. Here, the diaphragm S is driven by means of the mechanical system comprising members 59, 2d, and iii, the member it having a weight 23 attached. The coil is has its terminals c'onductively secured to terminal lugs it struck up from flat conduccars l ii that are embedded or molded in suitable grooves formed in the inner side of the diaphragm These grooves are preferably so located as not to extend beyond the edges of the housing H and are, therefore, closed and-protected by it. The conductors ill" terminate in enlarged porto make contact with the spring-like conductors 27 that engage therewith and are housed in cylindrical bores 28 formed in the end of the housing. H and having their axes terior ends of the bores 26 have reduced bores 29 so that it is substantially driving action is achieved;

to the sound to be reproduced are the moduspeaking device (not shown centrally placed penetrating further into the housing. This'penetration is suflicient to establish communication with the bores 30 that are parallel to he :rtudinal axis of the housl'ng and enter from the outside. The diameter of each of the bores 30 is sumcient to accommodate the terminals of those shown at it, which supply the electric impulses representing the sound to be reproduced. In each of the bores 28 is disposed a. plunger member 3| which is placed on the spring-like conductor 21in the bore and pressed against the end of the bore, each pler having a reduced portion 32 that is arranged to extend through the reduced bore 29 that communicates with the bore 30.. The extension oi the portion 32 is such as to penetrate only partially into the bore 30, in order thereby to make yielding but frictional contact with the terminal member that may be inserted therein.

. In each of the forms described, it is seen that an air gap of substantially constant dimensions is employed. In consequence, the performance of the device is substantially unaflected by the application of pressure to the diaphragm or extended vibated member. Such devices mayv hence be described as resistant to volume or tone change. By reason of this fact also it is practical to use such devices as variable range hearing aid devices for the hard of hearing. No matter how gripped or held, the mechanical perfonnance of such devices is substantially the same. By a suitable selection, however, of the range at which such device is used, the person using the same may achieve the effect of varying the effective air coupling, as pointed out above, and hence vary the quality of the sound perceived so as to obtain a desired eflect.

- It is seen, in consequence, that such devices are particularly adapted for use with group hearing aids, as, for example, in. theaters and motionpicture houses, where it is desired to have sound supplied from suitable outlets distributed around the theater. or moving-picture house. Since certain changes may be made in the above construction and different embodiments of the invention could he made without departing from the scope thereof, portioning the magnetic circuit so that when used on a hearing the battery operated type, battery current fiQWlllg through the .ac-= tuating winding would alter the constants from the desirable, but would malsean eficient substitute for the heavier and bulkier bi-polar ear-piece,- it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having; described my invention, what I claim as new and desire to secure by Letters Patent is: '1. In a loudspeaker, the combination of a portable enclosed at least one side of which forms an extended member adapted to be electrically vibrated for the propagation of sound at audible volume and at voice frequencies, a vibrating mechanism in the casing comprising members arranged in the form of a tuning fork, one of the prongs thereof being secured to the said extended member for reactively imparting vibrations thereto, electro-magnetic driving means disposed between the prong members of the said mechanism at the open end thereof, and means for imparting mechanical mass and stiffness to the said vibrating mechthe'conductors, such as for example, by pro anisrn to alter the frequency response 01' the system.

2. In a loudspeaker, the combination of a portable enclosing casing adapted to be bodily vibrated for the propagation of sound at audible volume and at voice frequencies through an elastic medium, at least one side of said casing being of extended area, and a vibrating mechanism in said casing comprising a massive ele- 0 ment, means connecting one portion of said 

